Concrete pipe having a liner of an epoxy resin-coal composition



1967 w. 'r M LAUGHLlN EIQ'AL 3,297,056

CONCRETE PIPE HAVING A LINER OF AN EPOXY RESIN-COAL COMPOSITION FiledDec. 13, 1963 2 Sheets-Sheet 1 INVENTORS WILLIAM TMcLAUGHLIN BY JOHN R.WEINERT KW @MV flTTOR/VEYS 1957 w. T. MCLAUGHLIN ETAL I ,0

CONCRETE PIPE HAVING A LINER OF AN EPOXY RESIN-GOAL COMPOSITION FiledDec. 13, 1963 r 2 Sheets-Sheet 2 L In 1g. E

' INVENTORS WILLIAM T.McLAUGHL|N BY JOHN RWEINERT 3,297,056 CQNCRETEPIPE HAVING A LINER @F AN EPOXY liilfiN-Cflhi. COMPOSHTHUN William T.Mcliaughiin and John R. Weinert, Pittsburgh,

Pa, assignors, by mesne assignments, to United States Steel Corporation,Pittsburgh, Pa, a corporation of Delaware Filed Dec. 13, M63, Ser. No.330,335 i Claims. (tCl. 133-445) This application is acontinuation-in-part of application, Serial No. 170,555, filed February2, 1962.

This invention relates to the preparation of an integral facing orbarrier on the interior surface of concrete pipes.

Concrete pipes are frequently subjected to service conditions whichcause attack on the inner surface of the pipe. Thus, hydrogen sulfide(and sulfuric acid formed therefrom) and other agents are released fromwater and sewage carried by such pipes. As a consequence, the art hasturned to vitrified clay in place of concrete in making hydrogen sulfideresistant pipes. Unfortunately, vitrified clay is relatively expensiveand does not have as good structural properties as desired, e.g., itscompressive strength is not as high as desired.

Concrete pipes further suffer from the disadvantage of having rough,porous interior surfaces and of having inadequate abrasion resistance.

It has been proposed to apply a protective ceramic plate or preformedsolid sheet of synthetic resin during the pipe manufacture. The use ofceramic plates has the disadvantage of high cost, both in the cost ofthe ceramic plates themselves and in their application to the concretepipe. In some instances the ceramic plate itself can be attacked bycorrosive agents. One of the most effective of the plastic sheets is aproduct known as T-Lock Amer-Plate which consists of a pigmented andp'lasticized polyvinyl chloride resin sheet having spaced T-shapedprotuberances on one side of the sheet for locking into the concrete.While T-Lock Arner-Plate has had some commercial success, it suffersfrom the disadvantage that it is only intermittent, mechanical lockingwith the concrete. Also, it must be seamed after application to theconcrete.

It is an object of the present invention to prepare a continuous,integral facing (lining) or barrier for the interior surface of concretepipe.

Another object is to prepare such a facing which is resistant tophysical and/or chemical agents which attack concrete itself either bycorrosion or erosion. I

A further object is to devise an economical way of applying a protectivefacing to the interior surface of wet or green concrete pipe.

An additional object is to develop an integral facing for the interiorsurface of concrete pipe to provide a product giving at least as goodprotection against hydrogen sulfide and sulfuric acid as vitrified clayand which gives a product structurally superior to vitrified clay, e.g.,it has better compressive strength.

Yet another object is to impart an abrasion resistant, non-porous,smooth facing to the interior surface of concrete pipe.

It is another object to provide a barrier to bridge and seal cracks orother imperfections, thus giving maximum protection against infiltrationor exfiltration through the pipe wall.

Still further objects and the entire scope of applicability of thepresent invention will become apparent from the detailed descriptiongiven hereinafter; it should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit 3,2fi7fi5fiPatented Jan. 10, 1967 and scope of the invention will become apparentto those skilled in the art from this detailed description.

It has now been found that these obiects can be attained by applying asettable epoxy resin composition onto the interior surface of a concretepipe while the concrete is still in the wet, green or uncured stage. Thepipe can be made by any conventional pipe forming machine, such ashorizontal centrifugal machines, vertical tamper machines and packerhead machines.

The settable epoxy resin composition can be applied by directlyimpinging the composition onto the wet, uncured surface, e.g. by forcingthe composition through a conduit which feeds into a spinning diskinside a wet, uncured concrete pipe. Centrifugal force throws thematerial against the pipe wall. The spinning disk is gradually retractedthrough the pipe in order to form a smooth facing or barrier over theentire pipe surface. There is a fusing or integration of the epoxy resincomposition facing into the pipe itself.

Alternatively the settable epoxy resin composition adhered (or cohered)to a solid surface or shield can be applied to the inner surface of aconcrete pipe while the concrete is still in the wet, uncured stage.Pressure is preferably applied by any convenient means to insure thereis penetration of the epoxy composition into the surface of the concreteto give a continuous, integral epoxy facing (lining). The concrete isthen allowed to cure in conventional fashion, either at atmospherictemperature or in a steam room. The epoxy resin composition also setswhile the concrete cures.

Unless it is desired to use the shield as the final interior corrosionresistant surface, the material of the outer surface of the shield isselected so that the adherence of the set plastic to the cured concreteis stronger than the adherence of the set plastic to the shield in orderthat the shield can be readily stripped away from the set plastic.

While the epoxy resin can be used alone it has been found much moredesirable to incorporate coal tar pitch in the epoxy formulation. It hasalso been found very desirable to include a finely divided mineralfiller such as sand.

The product of the present invention gives as good protection asvitrified clay and is structurally superior thereto. The conduit formedis not only resistant to hydrogen sulfide and sulfuric acid, but isabrasion resistant and presents a smoother surface than conventionalconcrete which has a rough texture. Surprisingly, the epoxy resin masticbonds to the wet, uncured concrete.

The invention will be best understood in connection with theaccompanying drawings wherein:

FIGURE 1 is a vertical elevation partially broken away of a tampermachine for use according to the invention;

FIGURE 2 is a view along the line 22 of FIGURE 1 after the concrete hasbeen poured;

FIGURE 3 is a vertical view partially broken away in section showing oneform of the invention;

FIGURE 4 is a fractional perspective view partially broken away and insection showing a cured concrete pipe having an integral, continuousinterior liner according to the invention;

FIGURE 5 is a vertical elevation of an alternative method of carryingout the invention;

FIGURE 6 shows a plural layer 01 laminate integral, continuous liningfor the interior surface of a concrete pipe;

FIGURE 7 shows a cured concrete pipe according to the invention prior toremoval of the shield; and

FIGURE 8 is a perspective view partially broken away showing theapplication of a settable plastic to the outside surface of a pipe.

There are numerous procedures for carrying out the invention. Several ofthese processes are described in further detail infra.

(1) The settable plastic can be applied directly to, e.g., sprayed on,the steel core of the concrete pipe forming machine prior to the pipeforming operation. The core preferably has a coating of a mold releaseagent. This procedure has the disadvantage as compared with some of theother procedures of the invention of tying up the pipe making machinefor considerable periods of time and also requires that the core becleaned. Additionally, it is more difiicult to obtain a smooth surfaceon the liner by this procedure than by procedures 2, 3 or 4.

(2) The settable plastic can be applied to a shield which has beenpreviously removably secured to the core of the pipe forming machine.The concrete pipe is then formed. Either before or after formation ofthe pipe, the shield is detached from the core and after formation theconcrete pipe-plastic liner and shield are removed from the machine andthe concrete allowed to cure. After the concrete has cured, the shieldis peeled away from the set liner which now adheres to the concrete.This procedure has the disadvantages of procedure 1 except that the coreneed not be cleaned. In procedure 1 and in one means of operatingprocedure 2 utilizing the temper machine the core is rotated during thepipe forming oper ation.

(3) The settable plastic is applied to the shield off the pipe formingmachine. The shield can then be placed on the pipe forming machine inthe manner described below. This is the preferred procedure. Preferably,the core is not rotated in procedure 3 when utilizing a damper machine.

A modified procedure 3a can be utilized to apply the integral liner toconcrete pipe made by a centrifugal horizontal machine (as well as pipemade by vertical machines). In the modified procedure the concrete pipeis first formed by the machine. While the pipe is still wet and green,i.e., uncured, the shield containing the settable plastic liningmaterial is placed inside the pipe. Then pressure is applied to theinterior surface of the shield, e.g., by an expandable mold, to forcethe settable plastic into integral, continuous contact with the innersurface of the concrete pipe, and the pipe is allowed to cure and theplastic to set. The shield is then peeled from the plastic liner whichnow is integrally and continuously united to the concrete pipe surface.

(4) A preformed liner of any desired polymer (resin or rubber) hasapplied thereto a surface activating coating, i.e., a settable plastic,of the same or diiferent material which will bind to the concrete. Theprocedure followed is tlfen the same as in procedure 3 except that thepreformed liner (shield) is not removed from the concrete pipe-setplastic surface. This method is suitable for making laminate linersintegrally and continuously united to the interior surface of concretepipe. Procedure 4 can be modified in a manner similar to procedure 3a.

(5) The settable plastic, i.e. epoxy resin formulation, e.g. a mixtureof coal tar pitch, epoxy resin and sand is charged into a cartridgewhich via a conduit feeds into a spinning disk. This assembly is loweredinside a wet, uncured concrete pipe. Material is extruded out of thecartridge onto the disk. Centrifugal force throws the material againstthe pipe wall as the assembly is gradually raised through the center ofthe stationary pipe. This procedure is disclosed more full in McLaughlinand Clancy application, Serial No. 330,416, filled December 13, 1963,entitled Facing of Concrete Pipe.

In a modification of procedure 5 the sand can be fed separately from theepoxy resin-coal tar pitch and the two streams integrated at any timeprior to application to the pipe wall.

Unless otherwise indicated, all parts and percentages are by weight.

In the illustrative examples described in connection with the drawingsthe settable plastic employed had the following composition:

Parts Liquid bisphenol A-epichlorhydrin having an epoxy equivalent ofabout 200 and a molecular weight of about 400 2.50 Butylglycidyl ether(to reduce the viscosity) 0.13 Diethylene triamine (catalyst) 0.20Pitch-containing coal tar specifically road tar Sand (filler) all passedthrough 30 mesh and substantially all retained on 200 mesh (Tylerscreen) 24.0

of about 400 2.63 Diethylene triamine (catalyst) 0.20 Pitch-containingcoal tar, specifically road tar Sand (filler) all passed through 20 meshand substantially all retained on 200 mesh (Tyler screen) 24.0

Composition C Parts Liquid bisphenol A-epichlorhydrin having an epoxyequivalent of about 250-280 and a molecular weight of about 500-560 2.50Butyl glycidyl ether (to reduce the viscosity) 0.13 Diethylene triamine(catalyst) 0.20 Pitchcontaining coal tar, specifically road tar Sand(filler) all passed through 30 mesh and substantially all retained on200 mesh (Tyler screen) 24.0

Referring more specifically to FIGURES 14 and 7 there is provided atamper type concrete pipe forming machine 2. The pipe forming machine 2includes a highly polished steel core 4 which is attached to shaft 6.The latter, in turn, is connected to any suitable power source, such asan electric motor, for raising and lowering the core 4. Attached to thetop of the core 4 is a bell former 8. The pipe forming machine 2 alsoincludes a platform 10 adapted for rotation. The platform 10 isconnected to any suitable means, e. g., an electric motor (not shown). Acylindrical piper form or mold 12 is positioned on the platform 10. Thepipe form is of conventional split mold construction. The pipe form ormold can be subsequently removed from the formed concrete pipe in eithercured or uncured condition by operating the handles 14 to open the mold.

After the pipe form 12 is placed on the platform 10, the cylindricalreinforcing cage 16 (made of an iron lattice) is positioned inside thepipe form. A cylindrical, free standing transfer medium or shield 18 isinserted inside the cage. The shield has an internal diameter such thatthe core 4 will closely fit inside it. The shield is made of a layer ofkraft paper board 20 having a thin protective coating of wax on itsinside surface to act as a moisture barrier. The outer surface of thekraft paper board is laminated to a 2 mil thick film of polyethylene 22.The outer surface of the polyethylene film is coated with Composition Ato form a layer 24 having a thickness of of an inch. Composition A canbe applied to the polyethylene by spraying, trowelling or otherconventional technique.

The core 4 is then lowered into the pipe form 12; until the plate 26attached to hell former 8 is in close proximity with the top of the pipeform.

At this point in the process the various pipe and liner media are in thefollowing relative positions indexed from the exterior inward: wall 28of the pipe form, open annular space 30, wire reinforcement cage 16,open annular space 32, coated shield 18 and core 4. With the core 4locked in a stationary position, the pipe form 12 is rotated asindicated by the arrow. Concurrently, wet concrete 34 is added via chute36 and tamper 38 driven by a motor (not shown) is activated. Tamper 38operates between the outside of the cage 16 and the inner wall of thepipe form 12. The tamper gradually rises in conventional fashion as thepipe form is filled with concrete. The tamper applies pressure to thewet concrete which aids in forcing the concrete into intimate,interlocking contact with the coating on the shield. The shield is sodesigned as to allow free movement around the stationary core, thuspreventing damage from the rotational shear forces to the masticComposition A which is to form the liner for the pipe. Filling andtamping of the concrete mix continues until the form is filled and thepipe socket 40 is formed. Then, as in conventional concrete pipe formingprocedure, the core is lifted from the pipe form and finished pipe, theshield and mastic liner are allowed to remain aflixed to the interiorpipe wall 42. Following removal of the pipe form from the pipe machine,the lined, uncured pipe, still encased in the form, is placed in a steamcuring chamber, the pipe form stripped off and the uncured, lined pipeput through the regular steam cure period, e.g., about 100 F. for 24hours. (As stated above, curing can also be accomplished under normalatmospheric conditions.) Following the steam cure, the shield isstripped from the inner wall of the pipe and, as shown in FIGURE 4, theprotective facing 24 made from set Composition A is a smooth, integrallyformed, continuously bonded protective interior wall 46 for the curedconcrete pipe 44-. As can be seen in FIGURE 4, the protective facing inthe forming period has been forced into the surface of the concrete tofill the pores therein. The irregularities normally present in theconcrete surface are elimi- Procedure 1 set forth above is illustratedby FIGURE 7 shows the shield being pulled away at the top from thefacing which is now integrally united to the cured concrete pipe.

Procedure 1 set forth above is illustrated by FIGURE 5. In this methodthe surface of the highly polished steel core is preferably treated witha thin film of a release agent, e.g., parafiin wax (although the releaseagent can be omitted). Then the core 4 is sprayed to approximate- 1y"has inch thickness with Composition A from spray gun 48. The sprayed-oncomposition is designated at 50. The pipe form 12 and Wire cage 16 arethen positioned on platform in the manner previously described inconnection with FIGURE 1 and the core is positioned on the platforminside the cage. The wet concrete is then poured with or withouttamping, although the latter is preferred and the pipe is produced. Thecore is allowed to rotate along with the pipe form and cage during theconcrete pouring operation. This is essential in this form of theinvention to prevent the mastic Composition A from being dispersedthroughout the concrete rather than forming the desired inner facing.Upon completion of the pour, the core is locked to prevent rotation andthe core is withdrawn. During the withdrawal, the formed pipe,protective Composition A and pipe form continue to rotate. The linedpipe is then cured in conventional fashion, e.g., by steam curing asdescribed above.

FIGURE 6 shows a portion of a finished concrete pipe having an integral,continuous laminated liner. This type of protected pipe can be preparedby the procedure described in connection with FIGURE 1 except that inplace of using a polyethylene coated kraft paper board shield there isprovided a shield made of a solid polymer which will adhere strongly tothe mastic composition and thus form a protective facing for theconcrete. Thus, in FIGURE 6 the finished concrete pipe 52 is laminatedto a phenolformaldehyde polymer liner 54 (or shield) by set CompositionA layer 56. The set Composition A not only is integrally andcontinuously united to the concrete pipe but also adheres strongly tothe polymer liner.

In another example Composition A was fed via a conduit into a diskspinning at 2800 r.p.rn. inside a wet, uncured 24 inch concrete pipe.The material was impinged by centrifugal force against the inner pipewall and impregnated the surface thereof and formed a contiguous smoothfacing mils thick on the Wall.

While the thickness of the facing was 110 mils in the specific examplesand usually is between 100 and mils, this can be varied widely. Thusfacings as thin as 10 mils or as thick as 300 or 400 mils or more can beformed on the wet, uncured concrete.

The epoxy resins which can be used include the epoxy ether resins havinga l,2-epoxy equivalency of greater than 1, such as the reaction productsof polyhydric alcohols or polyhydric phenols with epichlorhydrin orglycerol chlorhydrin. Examples of such resins are the polyglycidylethers of resorcinol, catechol, hydroquinone, bis-(4-hydroxyphenyl)-2,2-propane (bis-phenol A).4,4-dihydroxy-benzophenone, bis-(4-hydroxyphenyl) 1,1 ethane, tetrakis(4-hydroxyphenyl)ethane, bis-(4-hydroxyphenyl) -1,1-isobutane, bis(4-hydroxyphenyl) -2,2-butane, bis- (4hydroxy-Z-methylphenyl)-2,2-propane, bis-(4-hydroxy-Z-t-butylphenyl)-2,2-propane, bis-(Z-hydroxynaphyl)-methane, l,S-dihydroxy-naphthalene,ethylene glycol, propylene glycol, trimethylene glycol, diethyleneglycol, triethylene glycol, glycerol, dipropylene glycol, diglycerol,erythritol, mannitol, sorbitol, polyallyl alcohol, polyvinyl alcohol,novolak resins, e.g., the novolak from 4 moles of phenol and 3 moles offormaldehyde, as well as other novolaks having 3 to 7 phenolic nuclei,phloroglucinol, 2,4,4'-trihydro-xy diphenyl dimethyl methane,4,4'-dihydroxy diphenyl sulfone and 4,4-dihydroxy biphenyl. There canalso be used other epoxy resins and resin formers having a 1,2-epoxyequivalency of greater than 1 including polymeric butadiene dioxide,diglycidyl ether, allyl glycidyl ether, glycidyl methacrylate, glycidylester of trimerized linoleic acid, diglycidyl ester of dimerizedlinoleic acid, Oxiron 2000 (an epoxidized polybutadienepartiallyhydrolyzed vinyl acetate copolymer having a viscosity of 1800 poise, anepoxy equivalency of 177, having 2.5% hydroxyl and an iodine number ofWhile straight epoxy resins can be employed, preferably the epoxy resinsare modified with a bituminous material, most preferably, a coal tarpitch-containing material. The bituminous materials include coal tarpitch, refined coal tar, coal tar (which contains coal tar pitchtogether with more volatile organic materials), coal tar fractions, suchas RT-S and RT-9 (road tars), phenolic pitch, petroleum pitch, aromaticpetroleum pitches, pyrobitumen, straight run, blown, cracked, aromaticand polymerized asphalts, extract bitumen and pine tar. The preferredaromatic petroleum pitches are alkyl substituted polynuclear aromatichydrocarbons having a high degree of alkylation, the alkyl groups ingeneral having short chains, i.e. essentially not over propyl. Sucharomatic petroleum pitches usually have a boiling range of 480 1000 F.an aromatics content of over 90% and a parafiin of less than 8%, usuallyless than 6% and infrared indexes measured at 3.3 to 3.4 microns ofbetween 0.70 and 1.00. Typical commercial aromatic pitches in thiscategory are an aromatic petroleum pitch available from Monsanto andhaving an infrared index of 0.91 and Atlantic 100 resin having aninfrared index of 0.74.

It has also been found that coal can be used in place of the coal tarpitch. Either anthracite or bituminous coal can be used with thebituminous coal being preferred. The coal is normally ground to 20 meshor less.

Generally to 95 parts of bituminous material, cg. pitch or coal are usedwith 95 to 5 parts of epoxy resin.

Normally, there is also added 0.05 to 1 part of a curing agent per partof epoxy resin. Typical curing agents include diethylene triamine,triethylene tetramine, dicyandiamide, melamine, triethanolamine,N,N-dibutyl-1,3- propane diamine, amide from dimerized linoleic acid andethylene diamine phosphoric acid, aluminum chloride and otherFriedel-Crafts catalysts, oxalic acid, phthalic anhydride, etc.

There can also be added any of the conventional fillers, such as sand,coal, talc, mica, blast furnace slag, silica, clays, e.g., kaolin andbentonite, lignin, aluminum oxide, iron oxide, cement, silicon carbide,asbestos, diatomaceous earth, glass fibers. The filler can be from 1 to90% of the total composition. Desirably, sufficient filler, preferably asilica filler such as sand, is used to make a mastic composition.Preferably, 25 to 85% of finely divided inorganic filler is employed.The filler is preferably less than 20 mesh (Tyler screen). The preferredfillers are finely divided mineral fillers, e.g., sand.

There can also be added a thixotropic agent such as Cab-O-Sil (a flamehydrated silica) or Bentone 34 (dimethyl dioctadecyl ammoniumbentonite).

While the concrete pipe normally has the reinforcing wire therein, thiscan be omitted if desired.

The settable plastic, as used in the invention, is normally applied in asticky or mastic condition.

In the examples the pitch can be omitted, and the filler can also beomitted so that only the epoxy resin is .impinged on the interior pipewall to form the coating. Preferably, however, an aromatic pitch, suchas coal tar pitch, is included in the formulation and, as previouslystated, there is also preferably included sand or equivalent finelydivided mineral filler to impart a mastic consistency and abrasiveresistant quality to the composition.

Epoxy ether resins, particularly bis-phenol A-epichlorhydrin, are thepreferred resins, although other vicepoxy resins, i.e., oxirane groupcontaining resins, can be used, as previously indicated.

When a shield such as shield 54 is employed it can be made of a setepoxy resin of the type previously set forth.

The shield can also 'be made of a set polyester resin, e.g. a resin madefrom an unsaturated polyester and a polymerizable ethylenicallyunsaturated monomer. The polyester can be made from glycols such asethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, 2,3-butanediol, 1,3-butanediol, tetrachlorobutanediol-1,4,trimethylene glycol and unsaturated dibasic acids (and their anhydridesif available) such as maleic acid, fumaric acid, hexachloroendomethylenetetrahydro phthalic acid, cis-3,6-endomethylene-delta,4-tetrahydrophthalic acid, itaconic acid and citraconic acid. A portionof the unsaturated acid can be replaced by saturated aliphatic oraromatic polycarboxylic acids such as succinic acid, adipic acid,sebacic acid, azelaic acid, phthalic acid, tetrachlorophthalic acid,trimesie acid, hemimellitic acid and citric acid. As the ethylenicallyunsaturated monomer there can be used styrene, the vinyl toluenes, e.g.,p-vinyl toluene, alpha-methyl styrene, triallyl cyanurate, diallylphthalate, methyl methacrylate, ethylene glycol dimethacrylate, vinylacetate, o-chlorostyrene. A specific example of a polyester ispolyethylene glycol polypropylene glycol-adipate-maleate modified withstyrene.

Likewise the shield 54 can be made from polyurethanes, e.g.,the'reaction products of an organic polyisocyanate such as toluenediisocyanate, phenylene diisocyanate, naphthalene diisocyanate andhexamethylene diisocyanate with a polyhydric alcohol or polyester havingfree hydroxyl groups. Specific examples of such polyurethanes are madeby reacting toluene diisocyanate (a mixture of 80% of the 2,4-isomerWith 20% of the 2,6- isomer) with a polyester such as an ethyleneglycoladipate having a hydroxyl number of about 440 and an acid numberof about 1.5 or with a polyhydric alcohol such as LG-56(glycerol-propylene oxide adduct having a molecular weight of 3000),polypropylene glycol having a molecular weight of 2025, tris dipropyleneglycol phosphite, 1,2,6-hexane triol-propylene oxide adduct, molecularweight 1000, tris polypropylene glycol 2025 phosphite, a mixture ofpolypropylene glycol 2025 and tris dipropylene glycol phosphite.

The shield also can be made from other cured or thermoset resins such asalkyd resins, e.g. glyceryl phthalate, phenolic resins, e.g.,phenol-formaldehyde, cresol-formaldehyde, phenol-furfural,xylenol-formaldehyde, resorcinol-formaldehyde, aminotriazine-aldehyderesins, e.g., melamine-formaldehyde, urea-formaldehyde, polymerizedtriallyl cyanurate, dicyandiamide, diethylene glycol 'bisallylcarbonate, diallyl phthalate partial polymer, furane resins, e.g.,polymerized furfuryl alcohol, furfuryl alcohol-furfural copolymer,furfuryl alcoholurea-formaldehyde, and oxetane resins such as polymersof 3,3-dichloromethyl oxetane.

To make the shield 54 there can be used thermoplastic resins includingvinyl resins such as polystyrene, polyethylene, polypropylene,acrylonitrile-butadiene-styrene, polyvinyl chloride, vinylchloride-vinyl acetate copolymer, resinous polyoxymethylyene (Delrin),polycarbonates, e.g., bisphenol-A-polycarbonate (made from diphenylcarbonate and bisphenol-A), polyethylene terephthalate, polyamides andpolyester amides of the nylon type, e.g., polymeric hexamethyleneadipamide, vinylidene chloride resins (Saran), e.g., copolymer of 75%vinylidene chloride and 25% acrylonitrile, Teflon(polytetrafluoroethylene), Kel-F (polychlorotrifiuoroethylene), glass,vitrified clay, porcelain, thin gauge metal or rubbery materials such asnatural rubber, =butadiene-styrene copolymer, butadiene-acrylonitrilecopolymer, Butyl rubber (e.g. visobutylene-isoprene copolymer).

The shield or transfer medium 18 can be made of metal sheet, e.g.,steel, paper, fiber board, cloth or solid resin or elastomer. Therelease surface 22 can be polyethylene, polypropylene, Mylar(polyethylene terephthalate) or any other smooth surface to which thesettable plastic does not have as strong an adherence as is does to thecured concrete pipe.

As previously set forth, there can also be employed a release agent onthe core 4 When no shield is employed. Such release agent can be a Wax,polyethyl acrylate, a silicone (e.g., polymerized dimethyl siloxane).Such release agents can also be employed with the shield in place of thepolymer surface or in some instances can be used on top of the polymer,e.g., polyethylene, surface.

For many uses it is preferred that either no shield is employed or theshield is removed to expose the facing of epoxy resin composition.

While it is preferable to employ concrete there can be utilized moreexpensive but equivalent materials such as the hydraulic cements, e.g.,Portland cement and mag nesium oxychloride cement.

It may be noted, as is well known by those skilled in the art, that informing concrete pipe, e.g., by a vertical machine as described in thepresent application, there is a tendency for the aggregate to go to thecenter and for the portion of the pipe which forms the inner and outersurfaces to be made up essentially of the cement fraction of theconcrete, i.e., the center of the pipe is rich in aggregate Whereas thesurfaces are rich in cement.

While the present invention is primarily concerned with lining the innersurface of a concrete pipe, it can also be employed to line the outersurface of a concrete pipe. In such instance the shield rather thanbeing placed inside the cage and adjacent the core as shown in FIGURE 1would be placed outside the cage adjacent the mold form.

After positioning the shield having an internal coating of the coal tarepoxy mastic, the concrete is then poured in the same manner asdescribed in connection with FIGURE 1. The resulting product prior toremoval of the shield is shown in FIGURE 8 wherein pipe 70 has anexternal coating of coal tar-epoxy 72 which, in turn, is adhered to theshield comprising polyethylene layer 74 and kraft paper backing 76.After the pipe is cured and the plastic set, the shield is readilyremoved in the manner which has previously been indicated.

When the shield is placed adjacent the mold form, the tamping device 38can either be dispensed with or placed inside the cage. If the tampingdevice is positioned adjacent the shield, there is the danger that itwill pull on some of the settable plastic.

We claim:

1. A concrete pipe having an integral liner for the inner surfacethereof of a cured epoxy resin composition also including coal, saidepoxy resin composition having been applied to the inner surface of theconcrete pipe while the concrete was still in the Wet, uncured stage andsaid resin was in the settable stage.

2. A concrete pipe according to claim 1 wherein the coal is bituminouscoal.

References Cited by the Examiner UNITED STATES PATENTS 1,636,367 7/1927Illemann 138-145 X 2,120,309 6/1938 Carson 138-445 X 2,243,273 5/1941Edwards l38140 2,765,288 10/1956 Whittier et a1. 260-48 2,906,720 9/1959Simpson 260-28 SAMUEL ROTHBERG, Primary Examiner.

EDWARD V. BENHAM, LAVERNE D. GEIGER,

Examiners.

C. HOUCK, Assistant Examiner.

1. A CONCRETE PIPE HAVING AN INTEGRAL LINER FOR THE INNER SURFACETHEREOF OF A CURED EPOXY RESIN COMPOSITION ALSO INCLUDING COAL, SAIDEPOXY RESIN COMPOSITION HAVING BEEN APPLIED TO THE INNER SURFACE OF THECONCRETE PIPE WHILE THE CONCRETE WAS STILL IN THE WET, UNCURED STAGE ANDSAID RESIN WAS IN THE SETTABLE STAGE.